1. Field of the Invention
The invention relates to a porous silicate granular material, especially as aggregate for the production of construction materials such as lightweight concrete, mortar or heat-insulating plaster containing glass and a glassy crystalline component comprising 45 to 85 wt. % SiO2, 5 to 20 wt. % alkali oxide, 5 to 30 wt. % alkaline earth oxide and 2 to 30 wt. % of other oxides such as Al2O3 and/or Fe2O3, whereby the glassy crystalline component accounts for 5 to 75 wt. % of the granular material, and a method for producing such a granular material.
2. Description of the Related Art
Granular porous silicate construction materials or such materials occurring as granular material are used as aggregates for the production of lightweight concrete and lightweight mortars. In the production of close-grained and no-fines lightweight concretes these aggregates with their grain inherent strength and grain bulk density play a particular role. According to the prior art, grain inherent strengths and grain bulk densities can presently only be varied in certain ranges. For expanded glass granular material of grain group 4/8 mm for example, the grain strength based on DIN standard 4226, Part 3, is approximately 0.8 N/mm2 with a grain bulk density of 250 to 350 kg/m3. Corresponding pairs of values for expanded clays are: approximately 1.5 N/mm2xe2x80x94550 to 650 kg/m3, approximately 3.5 N/mm2xe2x80x94700 to 800 kg/m3 and approximately 5.3 N/mm2xe2x80x94900 to 1000 kg/m3.
DE 43 42 996 C2 discloses a method for producing foamed glass granular material as a lightweight aggregate from ground glass, binder and expanding agent. In this method recycled glass and additional components are mixed to a target composition containing (in wt. %) 68.5-75% SiO2, 10- less than 14 Na2O, up to 2.5% K2O, 1.8-3% Al2O3,  greater than 6-11% CaO, 0.5-4% MgO, up to 0.5% Fe2O3, up to 0.4% SO3, up to 1% TiO2, 0.5-3% BaO and up to 0.5% other components, whereby the alkali oxide component is less than 15 wt. %. This mixture is ground and then mixed intimately with the binder and the expanding agent. The mixture is then formed into pressings by means of press rollers at pressures of  greater than 100 to 200 MPa and the pressings are finally crushed to form raw granular material and aerated in a heat treatment method using controlled temperature regimes.
DE 198 36 869 A1 describes a method for producing starting products for glass products, glass-like materials or materials containing glass components or glass phase, especially lightweight aggregate for producing lightweight concrete, whereby a mixture of alkali silicates and alkaline earth silicates or alkali silicates, alkaline earth silicates and complex alkali-alkaline earth silicates and the corresponding hydrogen silicates or silicate hydrates and quartz is used. This method is essentially characterised by the fact that alkali hydroxides and alkaline earth oxides and hydroxides are mixed with powdered quartz, fine-grained silicon dioxide or SiO2-rich fine-grained materials with dissolving water or with the addition of water and if necessary with the addition of other raw or initial materials, especially glass powder, at temperatures between ambient temperature and 150xc2x0 C. and as a mixture are subjected to heat treatment involving silicate and hydrogen silicate formation, agglomeration and drying at temperatures between 80xc2x0 C. and 200xc2x0 C. Also described in DE 198 36 869 A1 are mixtures of fine quartz sand and cement as parting compounds for a granular material during a melt sintering process and an expanding process in a rotary kiln at temperatures of 850xc2x0 C. to 900xc2x0 C.
DE 197 02 560 A1 discloses a method for utilising old glass from cathode ray tubes. In this method a raw granular material is first manufactured to produce foamed glass granular material by adding a suitable parting compound such as chalk, cement or quartz powder so that the individual grains do not stick together during the subsequent expanding and sintering process. However, the possibilities for the use of cement are not exhausted thereby.
The influence of the atmosphere during the production of raw granular materials and during the melt sintering and expanding processes is not taken into account in the documents DE 43 42 996 C2, DE 197 02 560 A1 and DE 198 36 869 A1. Thus, the relevant control possibilities are also not taken into account.
The object of the present invention is to make available aggregates as porous silicate granular material having a dense surface and a broad spectrum of grain bulk density with high grain inherent strength which allow the required properties of lightweight concrete in terms of strength, bulk density and construction physics to be adjusted over a wide range.
It was found that this object is solved by a granular material of the type specified initially if the glassy crystalline component is the sinter reaction product of a mixture of
a) quartz powder and/or another essentially pure fine-grained SiO2 carrier,
b) powdered clay and/or powdered clay mineral,
c) Portland cement,
d) caustic soda and
e) an expanding agent as at least one additive.
The method for producing the granular material according to the invention is essentially characterised by the fact that a mixture of
a) powdered glass,
b) quartz powder and/or another essentially pure fine-grained SiO2 carrier,
c) powdered clay and/or powdered clay mineral,
d) Portland cement,
e) caustic soda,
f) an expanding agent and
g) water
and if necessary other additives and/or accessory agents is produced,
the mixture is agglomerated at a temperature of 20xc2x0 C. to 150xc2x0 C. at normal pressure with the water vapour partial pressure being adjusted, selected or controlled as a function of time-temperature and carbon dioxide being excluded or admitted, whereby the admission of carbon dioxide is controlled by adjusting or selecting the carbon dioxide partial pressure,
the intermediate product is crushed and graded if necessary, and the intermediate product thus obtained is heated at normal pressure with the carbon dioxide partial pressure and/or the water vapour partial pressure being adjusted, selected or controlled as a function of time-temperature, to a temperature of 700xc2x0 C. to 1250xc2x0 C. and sintered and expanded at this temperature.
The duration of the sintering and expanding process is usually between 5 minutes and 30 minutes.
The chemical composition of the glass component lies in the range of normal compositions of industrial bulk glasses, mainly the alkali-alkaline earth silicate glasses. The glassy crystalline component lies preferably in the composition range relative to mass of 45% to 85% SiO2, 5% to 20% alkali oxide (R2O), 5% to 30% alkaline earth oxide (RO), and 2% to 30% other oxides (such as Al2O3, Pe2O3).
Other objects and advantageous embodiments of the method will become apparent from a reading of the following detailed description and the appended claims.